Introduction
The SWL level of tidal-influenced outfalls (a total of 60, which showed a semi-diurnal pattern) were compared with NOAA 8454240 Philadelphia Tide Gage. The offset is determined by the differences in Peak tide levels between 12/1/2016 and 1/1/2017 (11 wet-weather days, 2.76 in precipitation.). Offsets are shown in below as a radial bar chart, of which larger than +/-1ft are highlighted in red.
Results
During this period, 11 outfalls fall off the +/-1ft boundary, which could be caused by:
1. The SWL sensor is installed further downstream from the SWO invert, which creates a positive offset, e.g., D42, D40, D02;
2. The SWL sensor is not attached to the SWO invert, which creates a negative offset, e.g., D70, D69, D48;
3. The outfall pipe hydraulics restricted the flow, which changes the amplitude of the recorded levels, e.g., D53, D21;
4. The SWL sensor is not calibrated, which creates a random offset and/or changes the amplitude of the recorded levels, e.g., D72.
To identify the source of offsets, assistance from the collectors might be needed.
Appendix: Individual Time-Series Plots
The time-series plots for the period between 12/1/2016 and 12/3/2016 are shown below (sorted by the significance of deviation):
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